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Null between 80 - 200Hz.

1niltothe

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Hi.

I have a pretty small room as a reference studio. Confession: I've set it up facing the long wall. Partly because the ceiling is raised, partly because of cupboards, windows and doors in the room. In terms of sound stage and general sound quality, it sounds a lot better than when I tried it the right way.

However, there's a vast, stubborn null. I'm pretty sure it's caused by boundary interference from the back wall (could be wrong). I have tried adjusting speaker height and distance from front and side walls, but null doesn't really budge.

I have a lot of 6" broadband fibreglass panels, including on the ceiling. Also have tried subwoofer placement, without much success thus far (could be there are spots that would help).

I have an acoustician coming over later in the week. He thinks it should be possible to figure something out. In the meantime I was curious to see if anyone has thoughts on what, if anything, might work - partly so I am not totally on the back foot and can discuss options with him.

I'll attach a sketch of the room dimensions. I have actually scooted the LP a lot further forward toward the speakers, which does make the bass null less severe.

Edit - I know the high end also has some null issues, but I'm not so worried about those at this point. Perhaps wrongly I see high end as a bit easier to manage.
 

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DjBonoBobo

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That measurement does not look right to me. How did you do the measurement and with which microphone? Was it a webcam or a cellphone that you measured with? Is this a sweep and what smoothing did you use?
I find it difficult to judge that way.

What speakers do you use?

And: How high is the room?
 

FeddyLost

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For proper assumptions would be nice to have more detailed drawing of all placements. Like distances from speakers and LP to walls and height of everything.
You can check if it's *BIR by placing sound source or sound receptor closer to the wall. *BIR null must move according to distance change.
Such sharp notch even after smoothing really looiks like destructive interference, but it can be a modal issue also.
You can also attach your mdat file and it can show more details.
 

rdenney

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A null at 120 Hz suggests an important first reflection path at 1.4 meters longer than the direct path to the speakers. This causes the 120-Hz sound to be one-half wavelength out of phase with the direct sound, and the two will cancel one another.

That first-reflection path could be from the floor, the side walls, the wall behind the speakers, or the wall behind the LP. If the latter two, the distance from the LP or speaker to the nearest wall will be 70 cm--a quarter wavelength--so that the reflected path will be half a wavelength longer.

Those are the things to look for.

Rick "who has a few nulls of his own" Denney
 

Lilith

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A null at 120 Hz suggests an important first reflection path at 1.4 meters longer than the direct path to the speakers. This causes the 120-Hz sound to be one-half wavelength out of phase with the direct sound, and the two will cancel one another.

That first-reflection path could be from the floor, the side walls, the wall behind the speakers, or the wall behind the LP. If the latter two, the distance from the LP or speaker to the nearest wall will be 70 cm--a quarter wavelength--so that the reflected path will be half a wavelength longer.

Those are the things to look for.

Rick "who has a few nulls of his own" Denney
What about the ceiling?
 

rdenney

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What about the ceiling?
Could be. I keep forgetting about ceilings, because the ceiling over my speakers slopes up so far that there simply is no first reflection to the listening position.

I just looked at numbers, and a ceiling 5 feet above the woofers will create a first reflection path 4.8 feet longer than a direct 8 feet to the listening position. 4.8 feet = 1.4 meters. If the woofers are 6 feet below the ceiling and the LP is 10 feet away, the extra distance is 1.7 meters, which would null at 200 Hz. But it seems that there are several common combinations of speaker height and listening distance that could couple with a standard ceiling to produce a null in that range.

Rick "easy to calculate" Denney
 

sarumbear

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Hi.

I have a pretty small room as a reference studio. Confession: I've set it up facing the long wall. Partly because the ceiling is raised, partly because of cupboards, windows and doors in the room. In terms of sound stage and general sound quality, it sounds a lot better than when I tried it the right way.

However, there's a vast, stubborn null. I'm pretty sure it's caused by boundary interference from the back wall (could be wrong). I have tried adjusting speaker height and distance from front and side walls, but null doesn't really budge.

I have a lot of 6" broadband fibreglass panels, including on the ceiling. Also have tried subwoofer placement, without much success thus far (could be there are spots that would help).

I have an acoustician coming over later in the week. He thinks it should be possible to figure something out. In the meantime I was curious to see if anyone has thoughts on what, if anything, might work - partly so I am not totally on the back foot and can discuss options with him.

I'll attach a sketch of the room dimensions. I have actually scooted the LP a lot further forward toward the speakers, which does make the bass null less severe.

Edit - I know the high end also has some null issues, but I'm not so worried about those at this point. Perhaps wrongly I see high end as a bit easier to manage.
I don't see nulls, all are standing wave peaks caused by the room modes. From the chart it looks like you have standing waves at roughly the following frequencies: 40Hz, 55Hz and 250Hz. If the chart doesn't change much around the listening area (or you only care about the listening position the chart reflects) then EQ will sort those peaks easily.
 

Frgirard

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Hi.

I have a pretty small room as a reference studio. Confession: I've set it up facing the long wall. Partly because the ceiling is raised, partly because of cupboards, windows and doors in the room. In terms of sound stage and general sound quality, it sounds a lot better than when I tried it the right way.

However, there's a vast, stubborn null. I'm pretty sure it's caused by boundary interference from the back wall (could be wrong). I have tried adjusting speaker height and distance from front and side walls, but null doesn't really budge.

I have a lot of 6" broadband fibreglass panels, including on the ceiling. Also have tried subwoofer placement, without much success thus far (could be there are spots that would help).

I have an acoustician coming over later in the week. He thinks it should be possible to figure something out. In the meantime I was curious to see if anyone has thoughts on what, if anything, might work - partly so I am not totally on the back foot and can discuss options with him.

I'll attach a sketch of the room dimensions. I have actually scooted the LP a lot further forward toward the speakers, which does make the bass null less severe.

Edit - I know the high end also has some null issues, but I'm not so worried about those at this point. Perhaps wrongly I see high end as a bit easier to manage.
Hi,

your measurements are unusable

you must measure each speaker in mono. In the same way as a speaker for an ear test, listen in mono
 

sarumbear

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I have a lot of 6" broadband fibreglass panels, including on the ceiling.
I forgot to add: there’s no such thing as broadband panel. They only work above a certain frequency. They hence, make the room sound unbalanced, which is bad. They should only be located at the correct point where reflections are happening. Everywhere else they mess the room sound. If your RT60 is high consider using diffusers instead.
 
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Frgirard

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I forgot to add: there’s no such thing as broadband panel. They only work above a certain frequency. They hence, make the room sound unbalanced, which is bad. They should only be located at the correct point where reflections are happening. Everywhere else they mess the room sound. If your RT60 is high consider using diffusers instead.

The reflection : the sound is not a rai but a front wave.
The rt60 : in domestic room is irrelevant.
6" plus air gap works above 100 Hz
The diffusers :except the polycylindrical diffuser, it's an error.
 

sarumbear

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The reflection : the sound is not a rai but a front wave.
The rt60 : in domestic room is irrelevant.
6" plus air gap works above 100 Hz
The diffusers :except the polycylindrical diffuser, it's an error.
I suggest you study acoustics.
 
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